1. Field of the Invention
This invention relates to densitometers for optically measuring a concentration of liquid or solid in a sample medium and, more particularly, to a densitometer for measuring a concentration of liquid or solid having the property that particle diameters of the liquid or solid being measured are changeable in response to an operation of an emulsifier.
2. Description of the Prior Art
A conventional densitometer for measuring a concentration of a liquid or solid on the basis of the turbidity of a fluid sample passing through an optical cell being measured on the basis of light transmitted through the sample fluid when it is illuminated with monochromatic light or white light has a disadvantage since various particle diameters of the liquid or solid in the sample fluid are dispersed at random therein, and it is, therefore, difficult to precisely measure the concentration via the turbidity of the sample fluid.
In order to avoid such disadvantage, it has been proposed to agitate a sample fluid by means of an ultrasonic wave or a mixer so as to obtain a uniform particle diameter and then optically measure the concentration via the turbidity of the sample fluid.
Such prior art method has encountered a difficult problem when a turbid ingredient produced from suspended solid formed of dust, dirt, etc. is mixed into the sample fluid, thereby involving a measurement error. One attempt has been made to eliminate this problem by measuring a turbid signal of a sample fluid before and after emulsification thereof and then calculating a difference between these two turbid signals thus removing the influence of the suspended solid upon the measurement. However, the turbid signal, which is a function of the detected transmitted light, changes in exponential function, so that it is difficult to remove the influence of the suspended solid upon the measurement by a calculation obtained from the difference between the two turbid signals.